Uniform hole doping in HgBa${}_2$Ca${}_2$Cu${}_3$O${}_{8+\delta }$ studied by ${}^{63}$Cu NMR

Abstract

We studied local magnetic properties of triple-CuO${}_2$-layer superconductors HgBa${}_2$Ca${}_2$Cu${}_3$O${}_{8+\delta }$ with rich ${}^{63}$Cu isotope (underdoped $T_{\mathrm{c}}$ = 124 K and optimally doped $T_{\mathrm{c}}$ = 134 K) by ${}^{63}$Cu NMR spin-echo techniques. The temperature dependences of the ${}^{63}$Cu nuclear spin-lattice relaxation rate ${}^{63}$(1/$T_1$) and the spin Knight shift ${}^{63}{K}_{\mathrm{spin}}$ of the inner plane Cu(1) site were nearly the same as those of the outer plane Cu(2) site in the normal states. The pseudogap temperature $T^{\ast }$ defined as the maximum temperature of ${}^{63}$(1/$T_{1}T$) was 190 K for the underdoped $T_{\mathrm{c}}$ = 124 sample and 143 K for the optimally doped $T_{\mathrm{c}}$ = 134 K sample. The NMR results indicate the uniform hole distribution in the three layers, which is consistent with a coalescence of three-derived Fermi surfaces predicted by a band theory. The room temperature in-plane ${}^{63}{K}_{\mathrm{spin}}^{ab}$ depends on whether the number of CuO${}_2$ planes per unit cell is even or odd for the Hg-based multilayer cuprate superconductors.

8 pages, 7 figures, to be published in J. Phys.: Conf. Ser. (2019)